1. Field of the Invention
The present invention relates to systems such as television systems used for displaying images encoded (or embedded) in a composite video signal, and more specifically to a method and apparatus for recovering the synchronization signals contained in composite video signals.
2. Related Art
Video signals typically contain display and non-display data. Display data generally represents images. Closed captioning data, teletext and electronic programing guide data are examples of non-display data. Video signals are usually generated at distant locations by broadcast companies or locally from devices such video cassette players (VCPs).
A television system (TV) typically receives video signals of a predetermined format and displays the encoded images. A TV may also recover and further process (including displaying) any non-display data. Other systems such as computer systems may also be designed to perform similar operations on a received video signal, as will be apparent to one skilled in the relevant arts.
Video signals are often generated and transmitted in composite format. That is, the same communication path and medium may be used for transmitting the data (display and/or non-display) and synchronization signals as is well known in the relevant arts. The data generally represents the color and luminosity of different portions of an encoded image and/or the other types of data as described above. The synchronization signals typically provide a time reference for recovering and further processing the embedded data.
As an illustration, a video signal may contain horizontal synchronization (HSYNC) signals for separating the display data portions corresponding to successive horizontal lines of an encoded image. Similarly, vertical synchronization signals (VSYNC) separate display data portions corresponding to successive image frames.
There is a need to recover the synchronization signals accurately from such composite video signals. For example, a sampling clock signal may be generated for sampling the display data signals. It is generally required that the sampling clock signal be synchronized accurately with the synchronization signals to enable the resulting sampled data values to represent the points of the encoded images correctly. At least for such a reason, there may be a need to accurately recover the synchronization signals.
Therefore, what is needed is a method and apparatus for accurately recovering the synchronization signals contained in composite video signals.